1. Field of the Invention
This invention relates to a process for the production of .kappa.-casein glycomacropeptide useful as a sialic-acid-conjugating sialic acid standard composition, which is used in assay kits for sialic acid, or as an infection protectant.
2. Description of the Prior Art
.kappa.-Casein glycomacropeptide (hereinafter abbreviated as ".kappa.-casein GMP") is a sialic-acid-conjugating peptide which is formed when rennin or pepsin is caused to act on .kappa.-casein in cow's milk. Cheese whey has been known for many years to contain .kappa.-casein GMP.
As a production method of .kappa.-casein GMP, it has been practised as a laboratory study to prepare .kappa.-casein GMP, for example, by causing pepsin to act on a solution of .kappa.-casein, which has been isolated from cow's milk, in deionized water, adding trichloroacetic acid to precipitate the para-.kappa.-casein fraction, dialyzing the resultant supernatant liquid against deionized water to desalt same, and then lyophilizing the resultant dialysate [Stan et al., "Bulletin of Experimental Biology and Medicine", 96, 889 (1983)] or by dissolving the above-mentioned .kappa.-casein in deionized water, adjusting the pH of the resultant solution to 6.7, causing rennet to act on the .kappa.-casein, adjusting the pH of the solution to 4.6 to precipitate and remove para-.kappa.-casein, subjecting the resultant supernatant liquid to dialysis to desalt same, and then lyophilizing the thus-prepared solution ["Milk Protein", page 200, Academic Press Inc.].
These methods are, however, for laboratory study and obviously cannot be said suitable for mass production.
On the other hand, no investigation has been made regarding the process for its mass production because no industrial utility has been known to date with respect to .kappa.-casein GMP.
It has however been reported recently that .kappa.-casein GMP is effective in lowering the appetite of dogs [Stan et al., "Bulletin of Experimental Biology and Medicine", 96, 889 (1983)]. It has hence been found that .kappa.-casein GMP can be used as a food additive for the prevention of overweight.
It has also been found that .kappa.-casein GMP is extremely effective as a standard composition for a kit for the assay of sialic acid. Besides, its various physiological activities are expected to find utility. There is hence an outstanding demand for its production on an industrial scale.